Drive control system for achieving target driveshaft power in a motor vehicle

ABSTRACT

An internal combustion engine (E) has associated control devices (ECU, GSCU, SCU) for controlling the engine in a manner such that the engine delivers a driving torque (CM) which is variable in dependence on predetermined measured parameters, in particular on the position (α) of the accelerator pedal (AP), and sensors (S1, S2) for detecting the position (α) of the accelerator pedal (AP), and the rate of rotation (ω M ) of the shaft (M) of the engine (E) or the forward speed (v) of the motor vehicle, respectively. The control system (ECU, GSCU, SCU) associated with the engine (E) is arranged:—to acquire from the sensors (S1, S2) the position (α) of the accelerator pedal (AP) and the rate of rotation (ω M ) of the engine (E), or the forward speed (v) of the motor vehicle;—to determine, in accordance with predetermined methods, the power (P T ) to be applied to the driving wheels in dependence on the measured position (α) of the accelerator pedal (AP) and on the calculated or acquired forward speed (v) of the vehicle, and to calculate, in dependence on the value determined for the power (P T ) to be applied to the driving wheels and on the forward speed (v) of the vehicle, the driving torque (C MREF ) which should correspondingly be delivered by the engine (E), and to control the engine (E) in a manner such that it delivers the driving torque (C MREF ) thus calculated.

This is a National stage entry under 35 U.S.C. §371 of Application No.PCT/EP00/06184 filed Jul. 3, 2000; the disclosure of which isincorporated herein by reference.

The present invention relates to a drive control system for a motorvehicle.

More specifically, the subject of the invention is a drive controlsystem for a motor vehicle, provided with:

an internal combustion engine with associated control means foroperating the engine in a manner such that the engine delivers a drivingtorque which is variable in dependence on predetermined measuredparameters, in particular on the position of an accelerator pedal, and

sensor means for providing electrical signals indicative of the positionof the accelerator pedal and of the rate of rotation of the shaft of theengine or of the forward speed of the motor vehicle.

WO-A-97 37 868 discloses such a system, in which the acceleratorposition and the vehicle speed are used to determine, from storedgraphs, the value of a correspondingly desired tractive force. Thelatter is multiplied by the vehicle speed to determine the correspondingvalue of the required power. At the same time the transmission ratio isshifted to an optimum ratio (if different therefrom), which isdetermined as a function of the accelerator position and the vehiclespeed. The torque to be delivered by the engine is then computed on thebasis of both the required power and the optimum transmission ratio.

EP-A-0 559 342 discloses a system for improving the fuel economy of acar equipped with an automatic transmission having a lock-up clutch. Thesystem controls both the engine and the automatic transmission on thebasis of a target driving torque corresponding to the stroke of theacceleration pedal.

U.S. Pat. No. 4,353,272 discloses a system for controlling theengine-transmission assembly of a motor-vehicle wherein the position ofthe accelerator defines the power setpoint of the engine.

According to the prior art, the command imparted by means of theaccelerator is interpreted by an engine management unit in accordancewith a so-called “driveability map” which is stored in a memory andwhich causes a predetermined driving torque delivered by the engine tocorrespond unequivocally to each position of the accelerator pedal andto each rare of rotation of the engine shaft.

According to the rate of revolution of the engine, the command impartedby the accelerator is thus “translated” by the engine management unitdirectly into a value of the driving torque delivered to the engineshaft. The power or the torque which is actually applied to the drivingwheels thus depends not only on the driving torque thus delivered by theengine but also on the transmission ratio put into effect by thegearbox.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an innovative drivecontrol system for a motor vehicle which, in particular, enables theengine to be managed with more degrees of freedom than with conventionalsystems. This and other objects are achieved, according to theinvention, by the system the main characteristics of which are definedin appended claim 1.

The control system according to the invention is applicable inparticular and advantageously to integrated drive control in a motorvehicle having a servo-assisted gearbox comprising an input shaft whichcan be coupled to the engine shaft by means of a servo-controlledclutch, and in which first and second electrically-operated actuatormeans are associated with the gearbox and with the clutch, respectively.

In motor vehicles having servo-assisted or “automatic” gearboxes, drivecontrol, that is, control of the power or torque applied to the drivingwheels and exchanged with the ground, is the combined result of thecommand imparted by the driver by means of the accelerator pedal and ofthe gear ratio selected by the driver.

In these motor vehicles, if the driver is not particularly skilled,drive control, that is, the torque actually applied to the drivingwheels and exchanged with the ground is not generally optimal.

A further object of he present invention is therefore to provide anintegrated drive control system which is better than the conventionalmethod of separate control of the engine and of the gearbox, permittingimproved and more direct control of the power applied to the drivingwheels, greater driving comfort and optimized use of the engine inaccordance with predetermined objectives such as a reduction inconsumption and/or exhaust emissions.

This and other objects are achieved, according to the invention, by anintegrated drive control system the main characteristics of which aredefined in appended claim 3.

As will be appreciated better from the following part of the presentdescription, a system of this type according to the invention is basedupon the concept of controlling, directly by means of the acceleratorpedal, the power which is applied to the driving wheels of the vehicleand not the driving torque delivered by the power unit. In other words,it is not purely and simply the engine which is controlled by the drivermeans of the accelerator pedal, but rather the dynamics of the forwardmovement of the vehicle.

Further characteristics and advantages of the invention will becomeclear from the following detailed description, given purely by way ofnon-limiting example, with reference to the appended drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a control system according to theinvention,

FIG. 2 is a block diagram which shows a possible architecture of anintegrated engine-control system and of a servo-assisted gearbox,according to the invention,

FIG. 3 is a graph which shows the correlation between the position ofthe accelerator pedal, the forward speed of the vehicle, and the powerapplied to the driving wheels, implemented in a system according to theinvention,

FIG. 3a shows curves of the torque delivered, as a function of the rateof rotation and with variations in the position of the acceleratorpedal, for a specific internal combustion engine.

FIG. 3b shows curves of the power applied to the driving wheels, as afunction of the forward speed of the vehicle and with variations in theposition of the accelerator pedal, for a specific engine/transmissionunit,

FIG. 4 is a graph relating to the method of bringing about a change oftransmission ratio, implemented in a system according to the invention,

FIG. 5 is a flow chart showing the way in which a system according tothe invention operates,

FIG. 6 is a further graph showing the curve of the longitudinalreference jerk as a function of the power applied to the wheels, used ina system according to the invention,

FIG. 7 is a schematic view of a transmission between the engine shaftand the driving wheels in a motor vehicle provided with a gearbox,

FIG. 8 is a set of graphs which show curves of rates of rotation andtorques, as functions of time given on the abscissa, in the course of agear change in a system according to the invention, and

FIG. 9 shows an alternative system architecture to that shown in FIG. 2.

In FIG. 1, the internal combustion engine of a motor vehicle isindicated E and its shaft is indicated M.

An electronic control unit ECU of known type is associated with theengine E. Various sensor devices are connected to the control unit ECU.In particular, a sensor S1 associated with the accelerator pedal AP ofthe motor vehicle is connected to the unit ECU. This sensor supplies tothe unit ECU signals indicative, for example, of the degree of operationα of the pedal, as a percentage, which is variable between 0% (pedalreleased) and 100% (pedal fully depressed).

A further sensor S2 supplies to the unit ECU signals indicative of therate of rotation ω_(M) of the shaft M of the engine E, that is, of thenumber of revolutions n of the shaft per unit of time.

DETAILED DESCRIPTION OF THE INVENTION

The control unit ECU is arranged to implement a procedure forcontrolling the torque C_(M) delivered to the shaft M by the engine E independence on the position α of the accelerator pedal AP, detected bymeans of the sensor S1.

For this purpose, an electronic memory M1 is associated with the unitECU and stores data for defining the power P_(T) to be applied to thedriving wheels of the motor vehicle in dependence on the position α ofthe accelerator pedal AP and on the longitudinal speed v of the motorvehicle. The data stored in the memory M1 defines a “driveability map”which will be described further below and which, in contrast withconventional engine-management systems, causes predetermined values ofthe power P_(T) which is to be applied to the driving wheels tocorrespond unequivocally to values of the position α of the acceleratorand to the forward speed v of the motor vehicle.

In other words, in engine management systems produced up to now, thecommand imparted by the accelerator pedal is interpreted in accordancewith a “driveability map” which correlates the position of the pedaldirectly with specific variables or parameters of the engine, inparticular, the number of revolutions n per unit of time and the drivingtorque C_(M) delivered to the shaft. In the system according to theinvention, the position α of the accelerator pedal AP is interpreteddifferently, that is, in accordance with a “driveability map” whichcorrelates the position α with variables or parameters relating to thedynamics of the vehicle, in particular to its forward speed v and to thepower P_(T) applied to the driving wheels.

The driveability map stored in the memory M1 is basically arepresentation, in the form of discrete values, of predetermined curvesfor the engine E, such as the curves shown by way of example in FIG. 3.These curves, which are predetermined, for example, in the manner whichwill be described below, correlate the position α of the acceleratorpedal with the power P_(T) to be applied to the driving wheels, for eachvalue of the forward speed v of the vehicle.

The control unit ECU is arranged to perform the following operationscyclically:

acquisition of the signals supplied by the sensors S1, S2, which areindicative of the position α of the accelerator pedal AP and of thenumber of revolutions n of the engine E per unit of time,

calculation of the forward speed v of the motor vehicle,

determination of the value of the power P_(T) to be applied to thewheels, by access to the driveability map held in the memory M1, on thebasis of the acquired value of the position α of the accelerator pedaland of the calculated value of the forward speed v of the motor vehicle;the determination of the value P_(T) generally involves interpolationbetween the discrete values stored in the memory,

calculation of the driving torque C_(MREF) to be delivered by the engineE, on the basis of the power value P_(T) determined in the previousstep,

control of the engine, E (injection of fuel, possibly advance of theignition, etc.) in a manner such that it delivers to the shaft M adriving torque equal to the torque C_(MREF) calculated.

As an alternative to the method set out above, the sensor S2 may be asensor which detects the forward speed and which can supply the unit ECUdirectly with the data relating to this speed which, in this case, doesnot therefore have to be determined by calculation.

Further characteristics of the control system according to FIG. 1 willbecome clear from the following description of an integrated drivecontrol system in a motor vehicle provided with a servo-assistedgearbox.

In FIG. 2, the internal combustion engine of a motor vehicle isindicated E. The shaft of the engine, indicated M, can be coupled to theinput shaft or primary shaft P of a gearbox G by means of a frictionclutch F. The gearbox G has an output shaft S which is coupled to thedriving wheels of the motor vehicle in a known manner, not shown.

The gearbox G is servo-assisted. Actuators A and B, associated with thefriction clutch F and, with the gearbox G, respectively, are, forexample, of the electro-hydraulic type and can bring aboutdisengagement/engagement of the clutch F and engagement/disengagement ofthe gears, respectively, under the control of a gear-shift control unitGSCU.

An electronic control unit ECU of known type is associated with theengine E. This unit can control the engine E in a manner such that theengine can deliver, by means of its shaft M, a driving torque which isvariable in dependence on predetermined measured quantities orparameters.

In the drive control system of FIG. 2, the control unit ECU of theengine E and the gear-shift control unit GSCU are in turn controlled bya system control unit SCU. Various sensor devices are connected to thissystem control unit. In particular, a sensor S1 associated with theaccelerator pedal AP of the motor vehicle is connected to the unit SCU.This sensor supplies to he unit SCU signals inddicative, for example, ofthe degree of operation α of the pedal, as a percentage, which isvariable between 0% (pedal released) and 100% (pedal fully depressed).

A further sensor S2 supplies to the unit SCU signals indicative of therate of rotation ω_(M) of the shaft M of the engine E, that is, of thenumber of revolutions n of the shaft per unit of time.

In this case also, the sensor S2 could alternatively be a sensor fordetecting the forward speed of the vehicle.

Further sensors, indicated Sn, are connected to the system control unitSCU in order to supply thereto signals indicative of the gear ortransmission ratio put into effect by the gearbox G.

The system control unit SCU is arranged to implement an automatic drivecontrol procedure, in particular, in dependence on the position of theaccelerator pedal AP detected by the sensor S1.

For this purpose, the unit SCU is associated with a first electronicmemory M1 in which data are stored for defining the power P_(T) to beapplied to the driving wheels of the motor vehicle, in dependence on theposition α of the accelerator pedal AP and on the longitudinal speed vof the motor vehicle. The data stored in the memory M1 define a“driveability map” which, as already stated with reference to the systemof FIG. 1, causes predetermined values of the power P_(T) to be appliedto the driving wheels a correspond unequivocally to values of theposition α of the accelerator and to the forward speed v of the motorvehicle.

The driveability map stored in the memory M1 is basically arepresentation, in the form of discrete values, of predetermined curvesfor the specific engine E and for the specific gearbox G associatedtherewith, such as the curves shown by way of example in FIG. 3. Thesecurves, which are predetermined, for example, in the manner which willbe described below, correlate the position α of the accelerator pedalwith the power P_(T) to be applied to the driving wheels, for each valueof the forward speed v of the vehicle.

The driveability curves shown in FIG. 3 have been determined in themanner which will now be described, for a specific engine-transmissionunit, in particular, for the following:

Diesel cycle internal combustion engine with “common rail” fuel supply,Fiat model DI/TCA M724, displacement 1.91 1;

Fiat C510 automatic gearbox with the following gear ratios:3.908-2.238-1.44-1.03-0.767 in gears 1-2-3-4-5, respectively,

axle ratio τ_(p)=3.15;

transmission efficiency η_(t)=0.95;

rolling radius of the wheels R=0.277 m;

moment of inertia of the wheels J_(W)=2.2465 Kg m².

FIG. 3a shows the characteristic curves of torque C_(M) as a function ofthe rate of revolution n (RPM) with variations in the acceleratorposition α (%), for the above-mentioned engine.

The characteristic torque curves shown in FIG. 3a correspondsubstantially to the “driveability map” conventionally used forconventional engine control in which the command imparted by theaccelerator pedal is interpreted substantially as a request for drivingtorque to be delivered by the engine.

The curves of FIG. 3a characterize the behaviour of the specific engineunder examination and can be derived experimentally in a manner known toexperts in the art.

FIG. 3a gives, in particular, the curves C_(MMAX) and C_(MMIN) whichdefine, respectively, the maximum torque and the minimum torque whichcan be delivered by the engine at the various rates of rotation.

The driving torque C_(M) delivered by the engine E and the rate ofrotation ω_(M) of the engine shaft are correlated with the torque C_(T)applied to the wheels and hence exchanged with the ground, as well aswith the forward speed v of the motor vehicle, by the followingequations:

C _(T) =C _(M)·η_(t)·τ_(p)·τ_(i)  (1)

v=ω _(M) ·R/(τ_(p)·τ_(i))  (2)

in which

η_(t) is the transmission efficiency,

τ_(p) is the axle transmission ratio,

τ_(i) is the transmission ratio engaged in the gearbox G, and

R is the rolling radius of the wheels.

By applying to the curves of FIG. 3a the transformation equations (1)and (2), as well as the known relationship which links power to torque,it is possible easily to obtain for the engine-transmission unit underexamination, the curves shown in FIG. 3b which express the power P_(T)applied to the wheels for each value of the forward speed v of thevehicle, with variations of the position α of the accelerator pedal. Inorder not to overburden the graphical representation, FIG. 3b gives thecurves of maximum power P_(TMAXi) (with i=1 to 5) and the curves ofminimum power P_(TMINI) (also with i=1 to 5) for each gear ortransmission ratio of the gearbox G.

Moreover, only the power curves relating to the accelerator pedalposition α=45% are shown specifically in FIG. 3b.

In order to define a driveability map in terms of power applied to thedriving wheels in dependence on the forward speed of the vehicle andwith variations of the accelerator pedal position, an examination ofFIG. 3b suggests, for example, that, at low values of the vehicle speed,in first gear, it may be advantageous to adopt, in the driveability mapto be implemented, a simple transposition of the original map C_(M)=f(n,α) into the corresponding variables P_(T), v, so that thecharacteristics with regard to the moving-off of the vehicle from astandstill, as well as the driveability characteristics at low speedsare kept unchanged. At faster speeds, in all of the gears ortransmission ratios, it is possible to prescribe in the driveability mapthat the power applied to the wheels P_(T) as the vehicle speed Vincreases should have a substantially constant or progressivelyincreasing curve in order to compensate partially for the resistance ofthe vehicle to forward movement.

With these criteria, it is possible, for example, to define thedriveability map shown in FIG. 3 from the graphs of FIG. 3b. Thisdriveability map is only one of the infinite number of possible mapswhich can be predetermined on the basis of widely varying criteria. Ingeneral, however, in defining the driveability map, the gear ratiosselected for the transmission can be left out of consideration. Thisindependence ensures continuity of torque upon changing from one gear toanother: in order to apply to the driving wheels the power P_(T)corresponding to a given accelerator pedal position α and to a givenforward speed v of the motor vehicle, any one of the possible gears thedomain (power, speed) of which contains the point under examination mayequally well be used.

In the system of FIG. 2, the driveability map stored in the memory M1 isformed in a manner such that the command imparted by the accelerator APis translated into the application of a power P_(T) to the wheels,irrespective of the gear ratio put into effect by the gearbox G.

By virtue of this fact, the selection of the gear or transmission ratiois no longer linked to subjective criteria dependent on the vehicleuser's driving style: since the power applied to the driving wheels isthat corresponding to the driver's “request”, effected by means of theaccelerator pedal, the gear ratio with which the power is achieved is ofsecondary importance. In this connection, naturally, there arelimitations:

for reasons of comfort (predominantly of an acoustic nature) it isnecessary to avoid gear changes at high rates of rotation of the engineE when possible, and

the frequency of gear changes should be kept as low as possible, forreasons of performance and comfort.

Once the two requirements given above have been satisfied, the selectionof the transmission ratio or gear to be put into effect can in principlebe performed with a certain amount of freedom, according to methodspredefined in order to achieve predetermined objectives such asminimizing fuel consumption and/or exhaust emissions.

For example, with the aim of minimizing fuel consumption, since thespecific consumption decreases as the load applied to the engine Eincreases, it is advantageous to use the highest possible gear, that is,the lowest possible transmission ratio, in any condition. Thistranslates into the need to use, as gear shifting boundary lines, thesame power curves relative to the various gears.

Possible criteria for selecting the gear shifting boundary lines inorder to minimize consumption are, for example, the following:

the transition between two adjacent gears or transmission ratios, bothwhen changing up and when changing down, is defined by a boundary linewhich, for positive values of the power P_(T) assigned to theaccelerator pedal position α, extends over a range of speeds of advanceof the vehicle which should be achievable within the maximum and minimumlimits of the power which can be produced by the engine, both with theoriginal gear and with the final gear,

for an upward gear shift, that is, for example, from second gear tothird gear, the gear shifting boundary one corresponds to the powercurve P_(T MAX) of the final gear, safeguarding the driveability of themotor vehicle, particularly at low rates of rotation of the engine E;

for downward gear shifts, that is, for example, from third gear tosecond gear, it is necessary to provide for a different boundary linefrom that provided for the corresponding upward gear shift (from secondgear to third gear) in order to avoid “overgearing” phenomena at theboundary line; for this purpose, a “hysteresis” is introduced byshifting the boundary line for the downward shift towards lower speedsof advance of the vehicle by a suitable amount.

The graph of FIG. 4 shows the boundary lines for the various gearshifts, obtained in accordance with the rules set out above for theengine-transmission unit defined above.

The gear shifting boundary lines shown in the graph of FIG. 4 can betranslated into a corresponding map of discrete values, for example, inaccordance with Table 1 below:

TABLE 1 Map of gear shifts for minimum consumption 1 → 2 2 → 1 2 → 3 3 →2 3 → 4 4 → 3 4 → 5 5 → 4 P_(T) V P_(T) V P_(T) V P_(T) V P_(T) V P_(T)V P_(T) V P_(T) V 0 15 0 7 0 23 0 19 0 33 0 28 0 44 0 39 11 15 11 10 1123 11 19 11 33 11 28 11 44 11 39 14 16 14 11 15 27 15 21 18 40 18 31 2056 20 46 20 19 20 12 20 30 20 23 20 42 20 32 21 58 21 48 30 24 30 15 3037 30 26 30 53 30 41 30 70 30 56 40 29 40 17 40 44 40 30 40 62 40 49 4084 40 64 50 35 50 19 50 55 50 37 50 77 50 57 50 102 50 80 60 35 60 19 5460 54 46 57 90 57 70 57 122 57 98 60 35 60 19 60 60 60 46 60 90 60 70 60122 60 98

The map or table given above is advantageously stored in a furthermemory M2 associated with the system control unit SCU (FIG. 2).

The way in which the above-described drive control system operates willnow be described in general terms with reference to the flow chart ofFIG. 5.

The system control unit SCU is arranged to perform the followingoperations cyclically:

acquisition of the signals supplied by the sensors S1 and Sn andindicative of the position α% of the accelerator pedal AP, and of thegear or transmission ratio τ_(i) currently engaged in the gearbox G (box10 of FIG. 5);

calculation of the forward speed v of the motor vehicle in accordancewith equation (2) given above, or acquisition of the speed value fromthe corresponding sensor (box 11);

determination of the value of the power P_(T) to be applied to thewheels, by accessing the driveability map contained in the memory M1, onthe basis of the acquired accelerator-pedal position valued and of thecalculated or acquired value of the forward speed v of the motorvehicle; the determination of the value P_(T) generally involvesinterpolation between discrete values stored in the memory (box 12);

calculation of the driving torque C_(MREF) to be delivered by the engineE, on the basis of the power value P_(T) determined the previous step,and by applying equation (1) given above (box 13);

determination of the necessary gear or transmission ratio τ_(n) by meansof the gear shifting map stored in the memory M2, on the basis of thecalculated or acquired value of the forward speed v and of the powervalue P_(T) determined (box 14);

checking whether the transmission ratio τ_(n) is equal to thetransmission ratio τ_(i) currently engaged (box 15);

if τ_(n)=τ_(i), the system control unit SCU supplies to the managementunit ECU of the engine E signals indicative of the calculated value ofthe required driving torque C_(MREF); the engine management unit ECUcontrols injection of fuel in a manner such that the engine E deliversthe driving torque C_(MREF) (box 16);

if τ_(n) is other than τ_(i), the system control unit SCU sends to thegear-shift control unit GSCU signals requesting a change of transmissionratio, with an indication of the ratio τ_(n) to be put into effect; thesystem control unit SCU also supplies to the engine management unit ECUand to the gear-shift control unit GSCU torque reference signalsindicative of the target driving torque value C_(MREF) to be deliveredby the engine E upon completion of the gear-shifting stage; thegear-shift control unit GSCU supervises the changing of the transmissionratio, controlling the actuators A and B associated with the clutch Fand with the gearbox G, respectively (box 17).

The gear-shift control unit GSCU may advantageously be arranged tosupervise the gear shift with the use of a simple mathematical model ofthe transmission of the motor vehicle which is valid for thegear-shifting stages.

The complexity of the gear-shift control results from the need tocoordinate the operation of the engine E and of the actuators A and Bassociated with the friction clutch F and with the gearbox G in a mannersuch as to achieve as comfortable and rapid a gear-shift transition aspossible.

The gear or transmission-ratio shifting operation involves basically thefollowing steps:

reduction of the driving torque C_(M) delivered by the engine E anddisengagement of the clutch F;

disengagement of the current gear, selection and engagement of the newgear, and

re-engagement of the clutch F and restoration of the driving torque.

In order to achieve a good compromise of gear shifting comfort withoutdetriment to performance, the control system must reduce the timerequired for the gear shifting operation as far as possible and mustmodulate the drive reduction and increase stages to take account of thedriver's “feel”.

In an embodiment which will now be described, this is achieved byimplementing a “jerk-oriented” strategy, that is, a strategy which tendsto reduce the jerk, that is, the time differential of the longitudinalacceleration of the motor vehicle.

It has in fact been found by statistical analyses that the jerk measuredis a good indicator of the degree of comfort of the gear shift perceivedby the passengers. The jerk is also a parameter which is correlated withthe driver's perception of gear shifting comfort. However, the driver'sjudgement is also affected by the integral of the longitudinalacceleration over the gear shifting period as a whole, which iscorrelated with a sensation of slowness.

In the drive control system according to the invention, the systemcontrol unit SCU may be arranged not only to decide on theimplementation of a gear shift in the manner described above, but alsoto assign a target value J_(REF) for the jerk during the gear-shiftstages.

For this purpose, the system control unit SCU may be associated with afurther memory M3 (FIG. 2) in which the target jerk values, as functionsof the power P_(T) to be applied to the wheels, derived experimentallywith a motor vehicle provided with the engine-transmission unit underconsideration, are stored.

On the basis of experimental measurements, it is possible, for example,to define a curve of target jerk values as functions of the power P_(T),for example, in accordance with FIG. 6. Values which represent the curveof jerk as a function of power P_(T) in discrete form are stored in thememory M3.

In order to implement a gear shifting procedure, the system control unitSCU also assigns to the gear-shift control unit GSCU the jerk referencevalue J_(REF) selected or determined by interpolation by access to thememory M3, on the basis of the power P_(T) required which has beendetermined in the manner described above.

The model of the engine/transmission/driving wheels unit which is usedto determine in real time the driving torque to be delivered by theengine E and the torque to be transmitted to the driving wheels during agear shifting stage is based on the basic diagram shown in FIG. 7 and onthe corresponding equations:

Clutch F Engaged

$\begin{matrix}{{{C_{M}(t)} - {C_{R}(t)}} = {\left( {J_{M} + J_{P}} \right) \cdot \frac{\omega_{M}}{t}}} & \text{(3)}\end{matrix}$

Clutch F Disengaged

$\begin{matrix}{{{C_{M}(t)} - {C_{F}\left( {X_{F}(t)} \right)}} = {J_{M} \cdot \frac{\omega_{M}}{t}}} & \text{(4)} \\{{{C_{F}\left( {X_{F}(t)} \right)} - C_{R}} = {J_{P} \cdot \frac{\omega_{P}}{t}}} & \text{(5)}\end{matrix}$

in which (see also FIG. 6):

C_(M), J_(M), ω_(M) are the torque delivered by the shaft M of theengine E, the moment of inertia of the engine shaft M, and the rate ofrotation of this shaft,

C_(F) and X_(F) are the torque transmitted by the friction clutch F tothe primary shaft P of the gearbox G and the position of the movablemember of the friction clutch F, respectively,

C_(R), J_(P), ω_(P) are the resisting torque on the primary shaft P ofthe gearbox G, the equivalent moment of inertia on the primary gearboxshaft P, and the angular velocity of the primary shaft, respectively.

With reference to equations (3) and (5) given above, the resistingtorque C_(R) may be considered, as a first approximation, to be constantduring gear shifting stages.

On the basis of equations (3) to (5), the individual stages of agear-shift can be analyzed as follows.

Torque Reduction Stage

With reference to FIG. 8, this stage lasts from an initial time to untila subsequent time t₁ and has a duration T_(U).

During this stage, the driving torque C_(M) has to be reducedprogressively to zero, starting from its initial value C_(M0). Thetorque C_(F) transmitted by the friction clutch F must simultaneouslyalso be reduced to zero, whilst still being kept equal to the drivingtorque C_(M), as shown in the lower graph of FIG. 8. During the torquereduction stage, the following are therefore the initial conditions:${t = {{t_{0}\text{:}\quad C_{M}} = C_{MO}}},{C_{R} = {C_{RO} = {C_{MO} - {\left( {J_{M} + J_{P}} \right) \cdot \frac{\omega_{M}}{t}}}}}$

and the following are the final conditions:

t=t ₁ : C _(M) =C _(F)=0

During the transition between t=t₀ and t=t₁, on the basis of equation(3) above, and upon the assumption that the resisting torque C_(R)remains constant: $\begin{matrix}{\frac{\omega_{M}}{t} = \frac{C_{M} - C_{RO}}{J_{M} + J_{P}}} & \text{(6)}\end{matrix}$

In equation (6), the moment of inertia J_(P) is that corresponding tothe transmission ratio τ_(i) which is engaged at the start of the gearshifting stage.

The longitudinal acceleration a_(x) of the motor vehicle is correlatedwith the angular acceleration of the shaft M of the engine E by means ofthe following equation: $\begin{matrix}{a_{x} = {{\frac{\omega_{w}}{t} \cdot R} = {{\frac{\omega_{M}}{t} \cdot \frac{R}{\tau_{i}}} = {\frac{C_{M} - C_{RO}}{J_{M} + J_{P}} \cdot \frac{R}{\tau_{i}}}}}} & \text{(7)}\end{matrix}$

where ω_(W) and R are the angular velocity and the rolling radius of thedriving wheels, respectively.

The jerk is the time derivative of the longitudinal acceleration a_(x):$\begin{matrix}{{jerk} = {\frac{a_{x}}{t} = {\frac{R}{\left( {J_{M} + J_{P}} \right) \cdot \tau_{i}} \cdot \frac{C_{M}}{t}}}} & \text{(8)}\end{matrix}$

In order for the jerk to remain constant and equal to the predeterminedreference value J_(REF) during this stage, the driving torque C_(M) mustdecrease in accordance with a linear curve. Since, upon completion ofthe torque reduction stage, the torque C_(F) transmitted by the frictionclutch F must also be zero, the same linear reduction curve also appliesto the torque C_(F), as shown in the left-hand portion of the lowergraph of FIG. 8. Thus: $\begin{matrix}{{C_{M}(t)} = {{C_{F}(t)} = {C_{MO} - {\frac{C_{MO}}{T_{C}} \cdot t}}}} & \text{(9)}\end{matrix}$

The duration T_(U) of the torque reduction stage is determinedunequivocally in accordance with equation (8) above, on the basis of theprescribed jerk reference value J_(REF):

T _(U) =C _(MO) ·R/J _(REF)·(J _(M) +J _(P))·τ_(i)  (10)

Synchronization Stage

During this stage, the friction clutch F is disengaged, the gear ratioτ_(i) is disengaged, and the new gear ratio τ_(n) is engaged.

During these operations, the angular velocity of the primary gearboxshaft P changes from ω_(W)τ_(i) to ω_(W)τ_(n), in a time which dependson the performance of the synchronizer and on the characteristics of theactuator A associated with the friction clutch F.

Upon completion of this stage:

t=t ₂:ω_(P)=ω_(W)(t ₂)·τ_(n)  (11)

Torque Re-application Stage

This stage (FIG. 8) has a duration of T_(L)=t₃−t₂.

During this stage, the driving torque C_(M) and the torque C_(F)transmitted by the friction clutch F have to synchronize the angularvelocities ω_(M) of the engine shaft and ω_(P) of the primary shaft P ofthe gearbox G in order to reach the previously calculated final valueC_(M REF) (box 13 of FIG. 5).

During this stage, the following are therefore the initial conditions:

t=t ₂ : C _(M) =C _(F)=0, C _(R) =C _(Ro)

and the following are the final conditions:

t=t ₃: ω_(M)=ω_(P) , C _(M) =C _(F) =C _(MREF)

During the transition, between the times t₂ and t₃, equation (5) givenabove applies and, upon the assumption that the resisting torque C_(R)remains constant and equal to the value C_(RO): $\begin{matrix}{\frac{\omega_{P}}{t} = \frac{C_{F} - C_{RO}}{J_{P}}} & \text{(12)}\end{matrix}$

where J_(P) is now calculated on the basis of the new transmission ratioτ_(n).

During this stage, the longitudinal acceleration a_(x) of the vehicleis: $\begin{matrix}{a_{x} = {{\frac{\omega_{w}}{t} \cdot R} = {{\frac{\omega_{P}}{t} \cdot \frac{R}{\tau_{n}}} = {\frac{C_{M} - C_{RO}}{J_{M} + J_{P}} \cdot \frac{R}{\tau_{n}}}}}} & \text{(13)}\end{matrix}$

Correspondingly, the jerk has the following expression: $\begin{matrix}{{jerk} = {\frac{a_{x}}{t} = {\frac{R}{\left( {J_{P} \cdot \tau_{n}} \right)} \cdot \frac{C_{F}}{t}}}} & \text{(14)}\end{matrix}$

In order also to keep the jerk value constant during this stage, it isnecessary to control both the driving torque CM and the torque CFtransmitted by the clutch F in accordance with linear curves, as shownin the right-hand portion of the lower graph of FIG. 8, so that:$\begin{matrix}{{C_{F}(t)} = {\frac{C_{MREF}}{T_{L}} \cdot t}} & \text{(15)} \\{{C_{F}(t)} = {{{\frac{C_{MREF}}{T_{L} - T_{M}} \cdot t}\quad {per}\quad t} > \left( {t_{2} + T_{M}} \right)}} & \text{(16.1)}\end{matrix}$

 C _(M)(t)=0 per t ₂ <t<(t ₂ +T _(M))  (16.2.)

The overall duration T_(L) of the torque re-application stage isdetermined on the basis of equations (14) and (15) and by prescribingthat the jerk should adopt the reference value J_(REF): $\begin{matrix}{T_{L} = \frac{C_{MREF} \cdot R}{J_{REF} \cdot J_{P} \cdot \tau_{n}}} & \text{(17)}\end{matrix}$

The period of time T_(M) represents the period necessary for the shaft Mof the engine E to slow down as a result of the torque transmitted bythe clutch F. This duration of this period is determined on the basis ofthe constraint relating to the synchronization of the angular velocityω_(M) of the engine shaft M with the angular velocity ω_(P) of theprimary gearbox shaft P.

The duration of the interval T_(M) can therefore be calculated bysolving a set of two equations corresponding to the time integrals ofequations (4) and (5) given above between t₂ and t₃. The solving of thisset of equations gives:

T _(M)=2J _(M)[ω_(M)(t ₂)−ω_(P)(t₂)]/C _(MREF) ++T·J _(M)[2C _(RO) /C_(MREF)−1]/J _(P)  (18)

The engine management unit ECU and the gear-shift control unit GSCU arearranged to implement the rules of variation given above for the drivingtorque C_(M) and the torque C_(F) transmitted by the clutch F.

The automatic drive control system described above may, however, beformed in a manner such as to permit “manual” control of theservo-assisted gearbox G, substantially in accordance with the priorart. For this purpose, a selector M/A (FIG. 2) operable manually by theuser in order to select the type of operation, that is, manual orautomatic, and additional sensor devices S_(M) for supplying to the unitSCU signals indicative of the transmission ratio which the driver wishesto engage, are also connected to the system control unit SCU. Thesensors S_(M) may be position sensors associated with devices of knowntype for selecting the transmission ratio, such as joystick-typedevices, push-buttons, or up/down selection levers.

In the “manual” operating mode, the system control unit SCU does notimplement the control methods described above, but is limited totransferring to the unit ECU the command imparted by the driver by meansof the accelerator pedal AP in order to obtain from the engine E thedriving torque C_(M) corresponding to the accelerator pedal position α,and to transferring to the gear-shift control unit GSCU signalsindicative of the transmission ratio which the driver wishes to engage.

The architecture of the control system shown in FIG. 2 is only one ofvarious possible architectures.

A further possible architecture is that shown in FIG. 9 in which partsand elements already described have again been attributed the samealphanumeric references as were used above.

In the arrangement according to FIG. 9, the functions of the controlunit SCU of FIG. 2 are divided between the engine E control unit ECU andthe gear-shift control unit GSCU, which are interconnected with eachother by means of a communication network CN, for example, of the CANtype. In particular, the memory M1 with the driveability map isassociated with the engine control unit ECU to which the sensors S1(position α of the accelerator pedal AP) and S2 (angular velocity ω_(M)of the shaft M of the engine E) are also connected.

The memory M2 (gear shifting map) and the memory M3 (jerk map) if it ispresent, as well as the sensor S_(n) (ratio τ_(i) engaged) and theselector M/A and the sensor S_(M), however, are associated with thegear-shift control unit GSCU.

During automatic, operation, the unit ECU calculates the forward speedv, determines the value of the power P_(T), and calculates thecorresponding torque C_(MREF). It transmits the value of the speed v andof the power P_(T) to the unit GSCU which determines the transmissionratio τ_(n) to be put into effect as well as the jerk reference valueJ_(REF) and then controls the change of transmission ratio, ifnecessary, substantially as described above, in coordination with theunit ECU.

Naturally, it is possible to adopt other architectures with differentdistributions of the tasks between the control units used, or even witha single control unit which controls the entire system alone.

What is claimed is:
 1. A drive control system for a motor vehicle,provided with: an internal combustion engine (E) with associated controlmeans (ECU, GSCU, SCU) for operating the engine in a manner such thatthe engine (E) delivers a driving torque (C_(M)) which is variable independence on predetermined measured parameters, in particular, on theposition (α) of the accelerator pedal (AP), and with sensor means (S1,S2) for providing electrical signals indicative of the position (α) ofthe accelerator pedal (AP) and of the rate of rotation (ω_(M)) of theshaft (M) of the engine (E) or of the forward speed (v) of the motorvehicle, respectively, the control means (ECU, GSCU, SCU) beingarranged: to acquire from the sensor means (S1, S2) the position (α) ofthe accelerator pedal (AP) and the rate of rotation (ω_(M)) of the shaft(M) of the engine (E), or the forward speed (v) of the motor vehicle, todetermine the power (P_(T)) to be applied to the driving wheels independence on the measured position (α) of the accelerator pedal (AP)and on the calculated or acquired forward speed (v) of the vehicle;characterized in that said control means (ECU, GSCU, SCU) are arrangedto calculate, in dependence on the value determined for the power (PT)to be applied to the driving wheels and on the forward speed (v) of thevehicle, the driving torque (C_(MREF)) which should correspondingly bedelivered by the engine (E), and to control the engine (E) in a mannersuch that it delivers the driving torque (C_(MREF)) thus calculated thesystem further comprising first memory means (M1) which are associatedwith the control means and in which there are stored data defining thepower (P_(T)) to be applied to the driving wheels of the vehicle independence on the position (α) of the accelerator pedal (AP) and on thelongitudinal speed (v) of the vehicle, the control means being arrangedto determine the power (P_(T)) to be applied to the driving wheels onthe basis of the data held in the first memory means (M1).
 2. A controlsystem according to claim 1, for a motor-vehicle provided with aservo-assisted gearbox (G) with an input shaft (P) which can be coupledto the shaft (M) of the engine (E) by means of a servo-assisted clutch(F), first and second electrically-operated actuator means (B, A) beingassociated with the gearbox (G) and with the clutch (F), respectively,and further sensor means (Sn) for supplying electrical signalsindicative of the transmission ratio (τ) engaged in the gearbox (G), thesystem being characterized in that the control means are arranged toimplement an automatic drive control procedure in dependence on theposition ( ) of the accelerator pedal (AP); the control means beingarranged, in particular, to acquire, from the sensor means (S1, S2, Sn)the position (α) of the accelerator pedal (AP), the rate of rotation(ω_(M)) of the shaft (M) of the engine (E), or the forward speed of themotor vehicle (v), and the transmission ratio (τ_(M)) put into effect bythe gearbox (G); to calculate or to acquire the forward speed (v) of thevehicle; to determine, in accordance with predetermined methods, thepower (P_(T)) to be applied to the driving wheels in dependence on thedetected position (α) of the accelerator pedal (AP) and on the forwardspeed (v) of the vehicle; to calculate, in dependence on the valuedetermined for the power (P_(T)) to be applied to the driving wheels andon the forward speed (v) of the vehicle, the driving torque (C_(MREF))which should correspondingly be delivered by the engine (E); todetermine, in accordance with predetermined methods, the transmissionratio (τ_(n)) to be put into effect by the gearbox (G), in dependence onthe value determined for the power (P_(T)) to be applied to the drivingwheels and on the forward speed (v) of the vehicle, and to check whetherthe transmission ratio (τ_(n)) to be put into effect corresponds to thetransmission ratio engaged (τ_(i)), and if the result is positive, tocontrol the engine (ECU) in a manner such that it delivers thecalculated driving torque (C_(MREF)), and if the result is negative, tocontrol the implementation of the change to the transmission ratio(τ_(n)) to be put into effect, controlling the engine (ECU) in a mannersuch that, upon completion of the operation to change to thetransmission ratio (τ_(n)) to be put into effect, the engine (E)delivers a driving torque substantially equal to the driving torque(C_(MREF)) calculated.
 3. A control system according to claim 2,comprising second memory means (M2) which are associated with thecontrol means and in which data are stored for defining the transmissionratio or gear (τ_(n)) to be put into effect by the gearbox (G) independence on the power (P_(T)) to be applied to the driving wheels andon the longitudinal speed (v) of the vehicle, and in which the controlmeans are arranged to determine the transmission ratio (τ_(n)) to be putinto effect on the basis of the data held in the second memory means(M2).
 4. A control system according to claim 2, in which the controlmeans are arranged: to determine, in accordance with predeterminedmethods, a reference value (J_(REF)) for the time differential of thelongitudinal acceleration (a_(x)) of the motor vehicle, in dependence onthe value determined for the power (P_(T)) to be applied to the drivingwheels, to generate reference signals indicative of a reference drivingtorque (C_(MREF)), and to control the change to the transmission ratio(τ_(n)) to be put into effect in a manner such as to keep the timederivative of the longitudinal acceleration (a_(x)) of the vehiclesubstantially constant and equal to the reference value (J_(REF)).
 5. Acontrol system according to claim 4, comprising third memory means (M3)which are associated with the control means and in which predeterminedvalues of the time differential of the longitudinal acceleration (a_(x))of the vehicle as a function of the power (P_(T)) to be applied to thedriving wheels are stored.
 6. A control system according to claim 4, inwhich the control means are arranged to control the engine (E) and theactuator means (A, B) associated with the clutch (F) and with thegearbox (G) during a gear shifting stage in a manner such that thedriving torque (C_(M)) delivered by the engine (E) and the torque(C_(F)) transmitted by the clutch (F) to the gearbox (G) vary inaccordance with respective substantially linear curves.
 7. A controlsystem according to claim 3, in which the second memory means (M2)contain, in the power to ground/forward speed plane (P_(T)/v), datarepresentative of gear shifting boundary lines, a boundary lineassociated with a shift from one gear to the immediately higher (lower)gear being different from that associated with the reverse change.
 8. Acontrol system according to claim 1, comprising manually-operatedselector means (M/A) for supplying the control means with signalsproviding selectively for manual drive control or for automatic drivecontrol.